Multiple spindle machines are known in the prior art. Multiple spindle machines are used to mass produce standardized types of components. Multiple spindle machines typically have several workstations at which machining operations are performed. A piece of raw stock, such as bar stock, enters the machine at a first station and as the machine indexes, various machining operations are performed. Once a station is indexed completely through the machine a completed part is formed. The part is released and the process is repeated for that station with a new piece of raw stock. The advantage of multiple spindle machines is that all stations in the machine are producing parts simultaneously, resulting in high production.
Multiple spindle machines typically have a large indexing drum with four, six or eight stations thereon. Each of the stations carries a work piece. In all but one of the stations, where a new piece of stock enters, a machining operation is performed. After each operation is completed the drum is rotated so that each work space moves sequentially through the location where the various operation is performed. Machining operations typically performed at a multiple spindle machine include turning and threading.
Most multiple spindle machines are very efficient in terms of producing standardized parts at a high rate. However, one draw back associated with multiple spindle machines is that the entire machine often operates off of a single main motor. The main motor simultaneously drives all the devices in the machine.
The speed of the multiple spindle machine typically changes from high speed to low speed and back again during the course of the operating cycle. High speed is typically used for times in the machine cycle where critical machining operations are not occurring. High speed operation is desirable when the machines are indexing or when the tools are moving to or away from the work pieces that are not performing work thereon. Low speed operation is used when the tools in the machine are forming the metal. As stated, threading operation of the bar stock is performed utilizing a threading die which is driven via a worm gear. In the prior art multiple spindle machines, such as the National Acme 7/16th inch RA-6 bar machine, the worm gear is driven through a threading clutch. The threading clutch acts to translate rotation from a reversible shaft to the threading shaft.
Referring now to FIG. 1, there is shown a prior art threading clutch 140 which is arranged generally surrounding a drive shaft 142. The drive shaft is operable through gearing to be rotated at high speeds in a forward and a reverse direction. The threading clutch is operable to selectively engage a connected gear with the drive shaft 142. In FIG. 1, threading clutch 140 is operable to engage high speed gear 144 through drive cup 146 with the threading shaft 148 when pressurized fluid is supplied via conduit 150. When the drive shaft is rotated in the forward direction the threading clutch is operable to translate the rotation of the drive shaft 142 to the reducing gear 152 through drive cup 154 to the threading shaft 148, while compressed fluid is supplied through conduit 150. In this arrangement the threading clutch is operable to translate a high speed gearing to the threading shaft 148 when it is desired to withdraw the threading die, whereas when the threading die is advanced into the stock the drive shaft rotation is translated via the reducing gear 152.
Referring now to FIG. 2, there is shown a cross sectional view of a prior art threading clutch. Specifically the threading clutch shown in FIG. 2 is that which is found in the National Acme 7/16th inch RA-6 bar machine. The actual size of this prior art threading clutch is approximately 2.5 inches in diameter and approximately 3.5 inches in length.
The threading clutch 160 comprises a first packet of friction disks 162 which are operable to engage the drive cup 146 of threading clutch 140 shown in FIG. 1. The threading clutch 160 further includes a second packet of friction disks 164 which is operable to engage the drive cup 154 of the threading clutch 140 shown in FIG. 1. Each packet of friction disks is operable to engage their respective drive cups when they are compressed. The threading clutch further includes a first piston 166 which is operably connected to the first packet of friction disks 162. The first piston 166 is slidably positioned within a first cavity 168 which communicates with a first port 170. Similarly the second packet of friction disks 164 are compressed via a second piston 172 which is housed within a second cavity 174 which communicates with a second port 176. Each of the drive cups 146 and 154 are engagably rotated with the shaft 178 by selectively supplying either first port 170 or the second port 176 with compressed fluid. The compressed fluid fills the respective cavity forcing the piston outward which causes the packet of friction disks to be compressed causing each of the friction disks, which are positively engaged with the drive cup to be rotated with the shaft 178.
There are several problems associated with the design and operation of the prior art threading clutch 160. The first problem is a lack of static torque capacity produced by the packets of friction disks. Torque capacity is a measure of the ability of the friction disks to translate the rotation of the shaft to the drive cups. The measure of torque capacity is that level at which the friction disks slip and fail to efficiently transfer the rotational power of the shaft. In this particular design the lack of torque capacity is due to the small piston area used to compress the packets of friction disks. The first and second pistons 166 and 172 use a small fraction of the available cross sectional diameter of the threading clutch 160 for purposes of supplying the force of compression for the friction disks.
Another major draw back with the prior art threading clutch design is that it is desirable to have the friction disks release the drive cups when the fluid pressure is vented from the respective piston cavity. In the prior art design the friction disks are prone to binding causing grinding and reduction of gear life.
Thus there exists a need in the prior art for a threading clutch apparatus which reliably translates the rotation of the shaft to the desired drive cup.